Mercury is the planet closest to the Sun in the Solar System, revolving around the Sun in 88 Earth days. The duration of one sidereal day on Mercury is 58.65 Earth days, and the solar day is 176 Earth days. The planet is named after the ancient Roman god of trade Mercury, an analogue of the Greek Hermes and Babylonian Nabu.
Mercury is an inner planet because its orbit lies within the orbit of the Earth. After Pluto was deprived of its planetary status in 2006, Mercury acquired the title of the smallest planet in the solar system. Mercury's apparent magnitude ranges from 1.9 to 5.5, but it is not easily visible due to its small angular distance from the Sun (maximum 28.3°). Relatively little is known about the planet yet. Only in 2009, scientists compiled the first full map Mercury, using images from Mariner 10 and Messenger. The presence of any natural satellites on the planet has not been detected.
Mercury is the smallest terrestrial planet. Its radius is only 2439.7 ± 1.0 km, which is less than the radius of Jupiter's moon Ganymede and Saturn's moon Titan. The mass of the planet is 3.3·1023 kg. The average density of Mercury is quite high - 5.43 g/cm3, which is only slightly less than the density of Earth. Considering that the Earth is larger in size, the density value of Mercury indicates an increased content of metals in its depths. The acceleration of gravity on Mercury is 3.70 m/s. The second escape velocity is 4.25 km/s. Despite its smaller radius, Mercury still exceeds in mass the satellites of the giant planets such as Ganymede and Titan.
The astronomical symbol of Mercury is a stylized image of the winged helmet of the god Mercury with his caduceus.
Planet movement
Mercury moves around the Sun in a fairly elongated elliptical orbit (eccentricity 0.205) at an average distance of 57.91 million km (0.387 AU). At perihelion, Mercury is 45.9 million km from the Sun (0.3 AU), at aphelion - 69.7 million km (0.46 AU). At perihelion, Mercury is more than one and a half times closer to Sun than at aphelion. The inclination of the orbit to the ecliptic plane is 7°. Mercury spends 87.97 Earth days on one orbital revolution. The average speed of the planet's orbit is 48 km/s. The distance from Mercury to Earth varies from 82 to 217 million km.
For a long time, it was believed that Mercury constantly faces the Sun with the same side, and one rotation around its axis takes the same 87.97 Earth days. Observations of details on the surface of Mercury did not contradict this. This misconception was due to the fact that the most favorable conditions for observing Mercury repeat after a period approximately equal to six times the rotation period of Mercury (352 days), therefore approximately the same section of the planet’s surface was observed at different times. The truth was revealed only in the mid-1960s, when radar surveys of Mercury were carried out.
It turned out that a Mercury sidereal day is equal to 58.65 Earth days, that is, 2/3 of a Mercury year. Such commensurability of the periods of rotation around the axis and revolution of Mercury around the Sun is a unique phenomenon for the Solar System. It is presumably explained by the fact that the tidal action of the Sun took away angular momentum and retarded the rotation, which was initially faster, until the two periods were related by an integer ratio. As a result, in one Mercury year, Mercury manages to rotate around its axis by one and a half revolutions. That is, if at the moment Mercury passes perihelion, a certain point on its surface is facing exactly the Sun, then at the next passage of perihelion, exactly the opposite point on the surface will be facing the Sun, and after another Mercury year, the Sun will again return to the zenith above the first point. As a result, a solar day on Mercury lasts two Mercury years or three Mercury sidereal days.
As a result of this movement of the planet, “hot longitudes” can be distinguished on it - two opposite meridians, which alternately face the Sun during Mercury’s passage of perihelion, and which, because of this, are especially hot even by Mercury standards.
There are no seasons on Mercury like on Earth. This occurs because the planet's rotation axis is at right angles to the orbital plane. As a result, there are areas near the poles that the sun's rays never reach. A survey carried out by the Arecibo radio telescope suggests that there are glaciers in this icy and dark zone. The glacial layer can reach 2 m and is covered with a layer of dust.
The combination of planetary movements gives rise to another unique phenomenon. The speed of rotation of the planet around its axis is practically constant, while the speed of orbital motion is constantly changing. In the orbital region near perihelion for approximately 8 days, the angular velocity of orbital motion exceeds angular velocity rotational movement. As a result, the Sun stops in the sky of Mercury and begins to move in the opposite direction - from west to east. This effect is sometimes called the Joshua effect, named after the main character in the Book of Joshua from the Bible, who stopped the movement of the Sun (Joshua 10:12-13). For an observer at longitudes 90° away from the “hot longitudes,” the Sun rises (or sets) twice.
It is also interesting that, although the closest orbits to Earth are Mars and Venus, Mercury is often the closest planet to Earth (since the others move away more, not being so “tied” to the Sun).
Anomalous orbital precession
Mercury is close to the Sun, so the effects of general relativity are manifested in its motion to the greatest extent among all the planets in the Solar System. Already in 1859, the French mathematician and astronomer Urbain Le Verrier reported that there was a slow precession in the orbit of Mercury that could not be fully explained by calculating the influence of the known planets according to Newtonian mechanics. The precession of Mercury's perihelion is 5600 arcseconds per century. Calculation of the influence of all other celestial bodies on Mercury according to Newtonian mechanics gives a precession of 5557 arcseconds per century. Trying to explain the observed effect, he suggested that there was another planet (or perhaps a belt of small asteroids) whose orbit was closer to the Sun than Mercury, and which was introducing a disturbing influence (other explanations considered the unaccounted for polar compression of the Sun). Thanks earlier achieved successes In the search for Neptune, taking into account its influence on the orbit of Uranus, this hypothesis became popular, and the desired hypothetical planet even received the name Vulcan. However, this planet was never discovered.
Since none of these explanations stood up to the test of observations, some physicists began to put forward more radical hypotheses that it was necessary to change the law of gravity itself, for example, change the exponent in it or add terms to the potential that depend on the speed of bodies. However, most of these attempts have proven controversial. At the beginning of the 20th century general theory relativity provided an explanation for the observed precession. The effect is very small: the relativistic "addition" is only 42.98 arcseconds per century, which is 1/130 (0.77%) of the total rate of precession, so it would take at least 12 million revolutions of Mercury around the Sun for perihelion to return to the position predicted classical theory. A similar, but smaller displacement exists for other planets - 8.62 arc seconds per century for Venus, 3.84 for Earth, 1.35 for Mars, as well as asteroids - 10.05 for Icarus.
Hypotheses for the formation of Mercury
Since the 19th century, there has been a scientific hypothesis that Mercury in the past was a satellite of the planet Venus, which was subsequently “lost” by it. In 1976, Tom van Flandern (English) Russian. and K.R. Harrington, on the basis of mathematical calculations, it was shown that this hypothesis well explains the large deviations (eccentricity) of the orbit of Mercury, its resonant nature of revolution around the Sun and the loss of angular momentum of both Mercury and Venus (the latter also - acquisition of rotation opposite to the main one in the Solar system).
Currently, this hypothesis is not confirmed by observational data and information from automatic stations on the planet. The presence of a massive iron core with a large amount of sulfur, the percentage of which is greater than in the composition of any other planet in the Solar System, the features of the geological and physical-chemical structure of the surface of Mercury indicate that the planet was formed in the solar nebula independently of other planets, that is Mercury has always been an independent planet.
Now there are several versions to explain the origin of the huge core, the most common of which says that Mercury initially had a ratio of the mass of metals to the mass of silicates that was similar to those in the most common meteorites - chondrites, the composition of which is generally typical for solid bodies of the Solar system and internal planets, and the mass of the planet in ancient times was approximately 2.25 times its present mass. In the history of the early Solar System, Mercury may have experienced an impact with a planetesimal of approximately 1/6 of its own mass at a speed of ~20 km/s. Most of the crust and upper layer of the mantle were blown into outer space, which, crushed into hot dust, were scattered in interplanetary space. But the core of the planet, consisting of heavier elements, has been preserved.
According to another hypothesis, Mercury formed in the inner part of the protoplanetary disk, which was already extremely depleted in light elements, which were swept out by the Sun into the outer regions of the Solar System.
Surface
In its physical characteristics, Mercury resembles the Moon. The planet has no natural satellites, but has a very thin atmosphere. The planet has a large iron core, which is the source of a magnetic field in its totality that is 0.01 of the Earth’s. Mercury's core makes up 83% of the planet's total volume. The temperature on the surface of Mercury ranges from 90 to 700 K (from +80 to +430 °C). The solar side heats up much more than the polar regions and the far side of the planet.
The surface of Mercury is also in many ways reminiscent of the Moon - it is heavily cratered. The density of craters varies in different areas. It is assumed that the more densely dotted areas with craters are more ancient, and the less densely dotted ones are younger, formed when the old surface was flooded with lava. At the same time, large craters are less common on Mercury than on the Moon. The largest crater on Mercury is named after the great Dutch painter Rembrandt, its diameter is 716 km. However, the similarity is incomplete - formations are visible on Mercury that are not found on the Moon. An important difference between the mountainous landscapes of Mercury and the Moon is the presence on Mercury of numerous jagged slopes, extending for hundreds of kilometers, called scarps. A study of their structure showed that they were formed during compression that accompanied the cooling of the planet, as a result of which the surface area of Mercury decreased by 1%. The presence of well-preserved large craters on the surface of Mercury suggests that over the past 3-4 billion years there was no large-scale movement of sections of the crust, and there was no erosion of the surface; the latter almost completely excludes the possibility of the existence of any significant atmosphere.
During research conducted by the Messenger probe, over 80% of the surface of Mercury was photographed and found to be homogeneous. In this way, Mercury is not similar to the Moon or Mars, in which one hemisphere is sharply different from the other.
The first data from a study of the elemental composition of the surface using the X-ray fluorescence spectrometer of the Messenger spacecraft showed that it is poor in aluminum and calcium compared to the plagioclase feldspar characteristic of the continental regions of the Moon. At the same time, the surface of Mercury is relatively poor in titanium and iron and rich in magnesium, occupying an intermediate position between typical basalts and ultramafic rocks such as terrestrial komatiites. Sulfur was also found to be relatively abundant, suggesting reducing conditions for planet formation.
Craters
Craters on Mercury range in size from small, bowl-shaped depressions to multi-ringed impact craters hundreds of kilometers across. They are in various stages of destruction. There are relatively well-preserved craters with long rays around them, which were formed as a result of the ejection of material at the moment of impact. There are also heavily destroyed remains of craters. Mercury craters differ from lunar craters in that the area of their cover from the ejection of matter upon impact is smaller due to the greater gravity on Mercury.
One of the most noticeable features of the surface of Mercury is the Plain of Heat (Latin: Caloris Planitia). This relief feature received this name because it is located near one of the “hot longitudes.” Its diameter is about 1550 km.
Probably, the body whose impact formed the crater had a diameter of at least 100 km. The impact was so strong that the seismic waves, having passed through the entire planet and focused at the opposite point on the surface, led to the formation of a kind of rugged “chaotic” landscape here. The force of the impact is also evidenced by the fact that it caused the ejection of lava, which formed high concentric circles at a distance of 2 km around the crater.
The point with the highest albedo on the surface of Mercury is the 60 km diameter Kuiper crater. This is probably one of the youngest large craters on Mercury.
Until recently, it was assumed that in the depths of Mercury there is a metallic core with a radius of 1800-1900 km, containing 60% of the planet’s mass, since the Mariner 10 spacecraft discovered a weak magnetic field, and it was believed that a planet with such a small size cannot have liquid kernels. But in 2007, Jean-Luc Margot's group summed up the results of five years of radar observations of Mercury, during which variations in the planet's rotation were noticed that were too large for a model with a solid core. Therefore, today we can say with a high degree of confidence that the planet’s core is liquid.
The percentage of iron in Mercury's core is higher than that of any other planet in the solar system. Several theories have been proposed to explain this fact. According to the most widely supported theory in the scientific community, Mercury originally had the same ratio of metal to silicates as a normal meteorite, having a mass 2.25 times greater than now. However, at the beginning of the history of the Solar System, a planet-like body with 6 times less mass and several hundred kilometers in diameter hit Mercury. As a result of the impact, much of the original crust and mantle was separated from the planet, causing the relative proportion of the core in the planet's composition to increase. A similar process, known as the giant impact theory, has been proposed to explain the formation of the Moon. However, the first data from a study of the elemental composition of the surface of Mercury using the AMS Messenger gamma spectrometer does not confirm this theory: the abundance of the radioactive isotope potassium-40 of the moderately volatile chemical element potassium compared to the radioactive isotopes thorium-232 and uranium-238 of the more refractory elements uranium and thorium does not cope with the high temperatures inevitable during a collision. It is therefore assumed that the elemental composition of Mercury corresponds to the primary elemental composition of the material from which it formed, similar to enstatite chondrites and anhydrous cometary particles, although the iron content of enstatite chondrites examined to date is not sufficient to explain the high average density of Mercury.
The core is surrounded by a silicate mantle 500-600 km thick. According to data from Mariner 10 and observations from Earth, the thickness of the planet's crust ranges from 100 to 300 km.
Geological history
Like the Earth, Moon and Mars, geological history Mercury is divided into eras. They have the following names (from earlier to later): pre-Tolstoyan, Tolstoyan, Kalorian, late Kalorian, Mansurian and Kuiper. This division periodizes the relative geological age of the planet. The absolute age, measured in years, is not precisely established.
After the formation of Mercury 4.6 billion years ago, the planet was intensively bombarded by asteroids and comets. The last major bombardment of the planet occurred 3.8 billion years ago. Some regions, for example, the Plain of Heat, were also formed due to their filling with lava. This led to the formation of smooth planes inside the craters, similar to those on the Moon.
Then, as the planet cooled and contracted, ridges and faults began to form. They can be observed on the surface of larger relief features of the planet, such as craters and plains, which indicates a later time of their formation. The period of volcanism on Mercury ended when the mantle had shrunk enough to prevent lava from reaching the planet's surface. This probably happened in the first 700-800 million years of its history. All subsequent changes in relief are caused by impacts of external bodies on the surface of the planet.
A magnetic field
Mercury has a magnetic field whose strength is 100 times less than that of Earth. Mercury's magnetic field has a dipole structure and highest degree symmetrically, and its axis deviates only 10 degrees from the axis of rotation of the planet, which imposes a significant limitation on the range of theories explaining its origin. Mercury's magnetic field may be generated by a dynamo effect, much like on Earth. This effect is the result of the circulation of the planet's liquid core. Due to the pronounced eccentricity of the planet, an extremely strong tidal effect occurs. It maintains the core in a liquid state, which is necessary for the dynamo effect to occur.
Mercury's magnetic field is strong enough to change the direction of the solar wind around the planet, creating a magnetosphere. The planet's magnetosphere, although small enough to fit inside the Earth, is powerful enough to trap plasma from the solar wind. Observations obtained by Mariner 10 detected low-energy plasma in the magnetosphere on the night side of the planet. Explosions of active particles were discovered in the magnetotail, indicating the dynamic qualities of the planet's magnetosphere.
During its second flyby of the planet on October 6, 2008, Messenger discovered that Mercury's magnetic field may have a significant number of windows. The spacecraft encountered the phenomenon of magnetic vortices - intertwined knots of the magnetic field connecting the ship with the planet’s magnetic field. The vortex reached 800 km in diameter, which is a third of the radius of the planet. This vortex form of magnetic field is created by the solar wind. As the solar wind flows around the planet's magnetic field, it binds and sweeps along with it, curling into vortex-like structures. These magnetic flux vortices form windows in the planetary magnetic shield through which the solar wind penetrates and reaches the surface of Mercury. The process of coupling between planetary and interplanetary magnetic fields, called magnetic reconnection, is a common phenomenon in space. It also occurs near the Earth when it generates magnetic vortices. However, according to Messenger observations, the frequency of reconnection of Mercury's magnetic field is 10 times higher.
Conditions on Mercury
Its proximity to the Sun and the planet's rather slow rotation, as well as its extremely weak atmosphere, mean that Mercury experiences the most dramatic temperature changes in the Solar System. This is also facilitated by the loose surface of Mercury, which conducts heat poorly (and with a completely absent or extremely weak atmosphere, heat can be transferred inward only due to thermal conductivity). The surface of the planet quickly heats up and cools down, but already at a depth of 1 m, daily fluctuations cease to be felt, and the temperature becomes stable, equal to approximately +75 ° C.
The average daytime surface temperature is 623 K (349.9 °C), the nighttime temperature is only 103 K (170.2 °C). The minimum temperature on Mercury is 90 K (183.2 °C), and the maximum, reached at noon at “hot longitudes” when the planet is near perihelion, is 700 K (426.9 °C).
Despite these conditions, there have recently been suggestions that ice may exist on the surface of Mercury. Radar studies of the planet's circumpolar regions have shown the presence of depolarization areas there from 50 to 150 km; the most likely candidate for a substance reflecting radio waves may be ordinary water ice. Entering the surface of Mercury when comets hit it, water evaporates and travels around the planet until it freezes in the polar regions at the bottom of deep craters, where the Sun never looks, and where ice can persist almost indefinitely.
When the Mariner 10 spacecraft flew past Mercury, it was established that the planet had an extremely rarefied atmosphere, the pressure of which was 5·1011 times less than the pressure of the Earth’s atmosphere. Under such conditions, atoms collide more often with the surface of the planet than with each other. The atmosphere is made up of atoms captured from the solar wind or knocked out from the surface by the solar wind - helium, sodium, oxygen, potassium, argon, hydrogen. The average lifetime of an individual atom in the atmosphere is about 200 days.
Hydrogen and helium likely enter the planet via the solar wind, diffuse into its magnetosphere, and then escape back into space. Radioactive decay of elements in Mercury's crust is another source of helium, sodium and potassium. Water vapor is present, released as a result of a number of processes, such as comet impacts on the surface of the planet, the formation of water from hydrogen in the solar wind and oxygen from rocks, and sublimation from ice that is found in permanently shadowed polar craters. The discovery of a significant number of water-related ions, such as O+, OH+ H2O+, was a surprise.
Since a significant number of these ions were found in the space surrounding Mercury, scientists hypothesized that they were formed from water molecules destroyed on the surface or in the exosphere of the planet by the solar wind.
On February 5, 2008, a group of astronomers from Boston University led by Jeffrey Baumgardner announced the discovery of a comet-like tail on the planet Mercury more than 2.5 million km long. It was discovered during observations from ground-based observatories in the sodium line. Before this, it was known about a tail no more than 40,000 km long. The team's first image was taken in June 2006 by the Air Force's 3.7-meter telescope on Mount Haleakala, Hawaii, and then used three smaller instruments, one at Haleakala and two at McDonald Observatory, Texas. A telescope with a 4-inch aperture (100 mm) was used to create images with a large field of view. The image of Mercury's long tail was taken in May 2007 by Jody Wilson (senior scientist) and Carl Schmidt (graduate student). The apparent length of the tail for an observer from Earth is about 3°.
New data about Mercury's tail appeared after the second and third flybys of the Messenger spacecraft in early November 2009. Based on these data, NASA employees were able to propose a model of this phenomenon.
Features of observation from Earth
Mercury's apparent magnitude ranges from -1.9 to 5.5, but it is not easily visible due to its small angular distance from the Sun (maximum 28.3°). At high latitudes, the planet can never be seen in the dark night sky: Mercury is visible for a very short period of time after dusk. The optimal time for observing the planet is morning or evening twilight during periods of its elongations (periods of Mercury's maximum distance from the Sun in the sky, occurring several times a year).
The most favorable conditions for observing Mercury are at low latitudes and near the equator: this is due to the fact that the duration of twilight there is shortest. In mid-latitudes, finding Mercury is much more difficult and is possible only during the period of best elongations, and in high latitudes it is impossible at all. The most favorable conditions for observing Mercury in the middle latitudes of both hemispheres occur around the equinoxes (the duration of twilight is minimal).
The earliest known observation of Mercury was recorded in the tables of Mul apin (a collection of Babylonian astrological tables). This observation was most likely made by Assyrian astronomers around the 14th century BC. e. The Sumerian name used for Mercury in the Mul Apin tables can be transcribed as UDU.IDIM.GUU4.UD ("jumping planet"). The planet was originally associated with the god Ninurta, and in later records it is called "Nabu" in honor of the god of wisdom and scribal arts.
IN Ancient Greece in the time of Hesiod, the planet was known by the names (“Stilbon”) and (“Hermaon”). The name "Hermaon" is a form of the name of the god Hermes. Later the Greeks began to call the planet "Apollo".
There is a hypothesis that the name “Apollo” corresponded to visibility in the morning sky, and “Hermes” (“Hermaon”) in the evening sky. The Romans named the planet after the fleet-footed god of commerce, Mercury, who is equivalent to Greek god Hermes, for moving across the sky faster than other planets. The Roman astronomer Claudius Ptolemy, who lived in Egypt, wrote about the possibility of a planet moving across the disk of the Sun in his work “Hypotheses about the Planets.” He suggested that such a transit had never been observed because a planet like Mercury was too small to observe or because the moment of transit occurred infrequently.
IN Ancient China Mercury was called Chen-hsing, "Morning Star". It was associated with the direction north, the color black and the element of water in Wu-hsing. According to the Hanshu, the synodic period of Mercury was recognized by Chinese scientists as equal to 115.91 days, and according to the Hou Hanshu - 115.88 days. In modern Chinese, Korean, Japanese and Vietnamese cultures, the planet began to be called “Water Star”.
Indian mythology used the name Budha for Mercury. This god, the son of Soma, was dominant on Wednesdays. In Germanic paganism, the god Odin was also associated with the planet Mercury and the environment. The Mayans represented Mercury as an owl (or perhaps as four owls, with two corresponding to the morning appearance of Mercury and two to the evening appearance), which was a messenger of the afterlife. In Hebrew, Mercury was called "Kokha in Hama."
Mercury in the starry sky (above, above the Moon and Venus)
In the Indian astronomical treatise "Surya-siddhanta", dating back to the 5th century, the radius of Mercury was estimated at 2420 km. The error compared to the true radius (2439.7 km) is less than 1%. However, this estimate was based on an imprecise assumption of the planet's angular diameter, which was taken to be 3 arcminutes.
In medieval Arab astronomy, the Andalusian astronomer Az-Zarqali described the deferent of Mercury's geocentric orbit as an oval like an egg or a pine nut. However, this conjecture had no impact on his astronomical theory and his astronomical calculations. In the 12th century, Ibn Bajja observed two planets as spots on the surface of the Sun. Later, the astronomer of the Maragha observatory Al-Shirazi suggested that his predecessor had observed the passage of Mercury and (or) Venus. In India, the astronomer of the Kerala school Nilakansa Somayaji (English) Russian. in the 15th century, developed a partially heliocentric planetary model in which Mercury revolved around the Sun, which in turn revolved around the Earth. This system was similar to that of Tycho Brahe, developed in the 16th century.
Medieval observations of Mercury in the northern parts of Europe were hampered by the fact that the planet is always observed at dawn - morning or evening - against the background of a twilight sky and quite low above the horizon (especially in northern latitudes). The period of its best visibility (elongation) occurs several times a year (lasting about 10 days). Even during these periods, it is not easy to see Mercury with the naked eye (a relatively dim star against a fairly light background of the sky). There is a story that Nicolaus Copernicus, who observed astronomical objects in the northern latitudes and foggy climate of the Baltic states, regretted that he had never seen Mercury in his entire life. This legend arose based on the fact that Copernicus’s work “On the Rotations of the Celestial Spheres” does not provide a single example of observations of Mercury, but he described the planet using the results of observations of other astronomers. As he himself said, Mercury can still be “caught” from northern latitudes by showing patience and cunning. Consequently, Copernicus could well have observed Mercury and observed it, but he described the planet based on other people’s research results.
Observations using telescopes
The first telescopic observation of Mercury was made by Galileo Galilei at the beginning of the 17th century. Although he observed the phases of Venus, his telescope was not powerful enough to observe the phases of Mercury. In 1631, Pierre Gassendi made the first telescopic observation of the passage of a planet across the disk of the Sun. The moment of passage was previously calculated by Johannes Kepler. In 1639, Giovanni Zupi discovered with a telescope that the orbital phases of Mercury were similar to those of the Moon and Venus. Observations have definitively demonstrated that Mercury orbits the Sun.
A very rare astronomical event is the overlap of one planet with the disk of another, observed from Earth. Venus occludes Mercury once every few centuries, and this event has only been observed once in history - on May 28, 1737 by John Bevis at the Royal Greenwich Observatory. Venus' next occultation of Mercury will be on December 3, 2133.
The difficulties accompanying the observation of Mercury have led to the fact that for a long time it was studied less than other planets. In 1800, Johann Schröter, who observed features on the surface of Mercury, announced that he had observed mountains 20 km high on it. Friedrich Bessel, using Schröter's sketches, erroneously determined the period of rotation around its axis to be 24 hours and the inclination of the axis to be 70°. In the 1880s, Giovanni Schiaparelli mapped the planet more precisely and proposed a rotation period of 88 days, coinciding with the sidereal period of revolution around the Sun due to tidal forces. The work of mapping Mercury was continued by Eugene Antoniadi, who in 1934 published a book containing old maps and his own observations. Many features of Mercury's surface are named after Antoniadi's maps.
Italian astronomer Giuseppe Colombo (English)Russian. noticed that the rotation period was 2/3 of the sidereal period of rotation of Mercury, and suggested that these periods fall into a 3:2 resonance. Data from Mariner 10 subsequently confirmed this point of view. This does not mean that Schiaparelli and Antoniadi's maps are incorrect. It’s just that astronomers saw the same details of the planet every second revolution around the Sun, entered them into maps and ignored observations at a time when Mercury was facing the Sun on the other side, since due to the geometry of the orbit at that time the conditions for observation were bad.
The proximity of the Sun also creates some problems for the telescopic study of Mercury. For example, the Hubble telescope has never been used and will not be used to observe this planet. Its device does not allow observations of objects close to the Sun - if you try to do this, the equipment will suffer irreversible damage.
Mercury Research modern methods
Mercury is the least studied terrestrial planet. In the 20th century, radio astronomy, radar and research using spacecraft were added to the telescopic methods of studying it. Radio astronomy measurements of Mercury were first made in 1961 by Howard, Barrett and Haddock using a reflector with two radiometers mounted on it. By 1966, based on the accumulated data, good estimates of the surface temperature of Mercury were obtained: 600 K at the subsolar point and 150 K on the unlit side. The first radar observations were carried out in June 1962 by V. A. Kotelnikov’s group at the IRE; they revealed the similarity of the reflective properties of Mercury and the Moon. In 1965, similar observations at the Arecibo radio telescope led to an estimate of Mercury's rotation period: 59 days.
Only two spacecraft were sent to explore Mercury. The first was Mariner 10, which flew past Mercury three times in 1974-1975; the closest approach was 320 km. The result was several thousand images covering approximately 45% of the planet's surface. Further research from Earth showed the possibility of the existence of water ice in polar craters.
Of all the planets visible to the naked eye, only Mercury has never had its own artificial satellite. NASA is currently conducting a second mission to Mercury called Messenger. The device was launched on August 3, 2004, and in January 2008 it made its first flyby of Mercury. To enter orbit around the planet in 2011, the device performed two more gravity assist maneuvers near Mercury: in October 2008 and in September 2009. Messenger also performed one gravity assist maneuver near Earth in 2005 and two near Venus in October 2006 and June 2007, during which it tested its equipment.
Mariner 10 is the first spacecraft to reach Mercury.
The European Space Agency (ESA), together with the Japanese Aerospace Exploration Agency (JAXA), is developing the Bepi Colombo mission, consisting of two spacecraft: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). The European MPO will explore Mercury's surface and depths, while the Japanese MMO will observe the planet's magnetic field and magnetosphere. BepiColombo is scheduled to launch in 2013, and in 2019 it will enter orbit around Mercury, where it will split into two components.
The development of electronics and computer science has made it possible to ground-based observations of Mercury using CCD radiation detectors and subsequent computer processing of images. One of the first series of observations of Mercury with CCD receivers was carried out in 1995-2002 by Johan Varell at the observatory on the island of La Palma on a half-meter solar telescope. Varell selected the best shots without using computer mixing. The reduction began to be applied at the Abastumani Astrophysical Observatory to series of photographs of Mercury obtained on November 3, 2001, as well as at the Skinakas Observatory of the University of Heraklion to series from May 1-2, 2002; To process the observation results, the correlation combination method was used. The resulting resolved image of the planet was similar to the Mariner 10 photomosaic; the outlines of small formations measuring 150-200 km in size were repeated. This is how a map of Mercury was compiled for longitudes 210-350°.
On March 17, 2011, the interplanetary probe Messenger entered Mercury orbit. It is assumed that with the help of equipment installed on it, the probe will be able to explore the landscape of the planet, the composition of its atmosphere and surface; Messenger's equipment also allows for research into energetic particles and plasma. The service life of the probe is determined to be one year.
On June 17, 2011, it became known that, according to the first studies carried out by the Messenger spacecraft, the planet’s magnetic field is not symmetrical relative to the poles; Thus, different numbers of solar wind particles reach Mercury's north and south poles. A prevalence analysis was also carried out chemical elements on the planet.
Features of the nomenclature
The rules for naming geological objects located on the surface of Mercury were approved at the XV General Assembly of the International Astronomical Union in 1973:
The small crater Hun Kal (indicated by an arrow), serving as a reference point for Mercury's system of longitudes. Photo by AMS Mariner 10
The largest object on the surface of Mercury, with a diameter of about 1300 km, was given the name Heat Plain, since it is located in the region of maximum temperatures. This is a multi-ring structure of impact origin, filled with solidified lava. Another plain, located in the region of minimum temperatures, near the north pole, is called the Northern Plain. Other similar formations were called the planet Mercury or an analogue of the Roman god Mercury in the languages of different peoples of the world. For example: Suisei Plain (planet Mercury in Japanese) and Budha Plain (planet Mercury in Hindi), Sobkou Plain (ancient Egyptian planet Mercury), Plain Odin (Norse god) and Tire Plain (ancient Armenian deity).
Mercury's craters (with two exceptions) are named after famous people in the humanitarian field of activity (architects, musicians, writers, poets, philosophers, photographers, artists). For example: Barma, Belinsky, Glinka, Gogol, Derzhavin, Lermontov, Mussorgsky, Pushkin, Repin, Rublev, Stravinsky, Surikov, Turgenev, Feofan the Greek, Fet, Tchaikovsky, Chekhov. The exceptions are two craters: Kuiper, named after one of the main developers of the Mariner 10 project, and Hun Kal, which means the number “20” in the language of the Mayan people, who used the base-20 number system. The last crater is located near the equator at meridian 200 west longitude and was chosen as a convenient reference point for reference in the coordinate system of the surface of Mercury. Originally craters bigger size names of celebrities were assigned who, in the opinion of the IAS, had respectively higher value in world culture. The larger the crater, the stronger the influence of the individual on the modern world. The top five included Beethoven (643 km in diameter), Dostoevsky (411 km), Tolstoy (390 km), Goethe (383 km) and Shakespeare (370 km).
Escarps (ledges), mountain ranges and canyons are named after ships of explorers who made history because the god Mercury/Hermes was considered the patron saint of travelers. For example: Beagle, Zarya, Santa Maria, Fram, Vostok, Mirny). An exception to the rule are two ridges named after astronomers, the Antoniadi Ridge and the Schiaparelli Ridge.
Valleys and other features on Mercury's surface are named after large radio observatories, in recognition of the importance of radar in planetary exploration. For example: Highstack Valley (radio telescope in the USA).
Subsequently, in connection with the discovery of grooves on Mercury by the automatic interplanetary station “Messenger” in 2008, a rule was added for naming grooves that receive the names of great architectural structures. For example: Pantheon on the Plain of Heat.
Mercury is the planet that is closest to the Sun. There is practically no atmosphere on Mercury, the sky there is dark as night and the Sun always shines brightly. From the planet's surface, the Sun would appear 3 times larger in size than Earth's. Therefore, temperature differences on Mercury are very pronounced: from -180 o C at night to unbearably hot +430 o C during the day (at this temperature lead and tin melt).
This planet has a very strange account of time. On Mercury, you will have to set the clocks so that a day lasts about 6 Earth months, and a year lasts only 3 (88 Earth days). Although the planet Mercury has been known since ancient times, for thousands of years people had no idea what it looked like (until NASA transmitted the first images in 1974).
Moreover, ancient astronomers did not immediately understand that they saw the same star in the morning and evening. The ancient Romans considered Mercury the patron of trade, travelers and thieves, as well as the messenger of the gods. It is not surprising that a small planet, quickly moving across the sky following the Sun, received his name.
Mercury is the smallest planet after Pluto (which was declassified as a planet in 2006). The diameter is no more than 4880 km and is quite a bit larger than the Moon. Such a modest size and constant proximity to the Sun create difficulties for studying and observing this planet from Earth.
Mercury also stands out for its orbit. It is not circular, but more elongated elliptical, when compared with other planets of the solar system. The minimum distance to the Sun is approximately 46 million kilometers, the maximum is approximately 50% greater (70 million).
Mercury receives 9 times more sunlight than the surface of the Earth. The lack of an atmosphere to protect from the burning rays of the sun causes surface temperatures to rise to 430 o C. This is one of the hottest places in the Solar System.
The surface of the planet Mercury is the personification of antiquity, not subject to time. The atmosphere here is very thin, and there has never been any water at all, so erosion processes were practically absent, except for the consequences of the fall of rare meteorites or collisions with comets.
Gallery
Did you know...
Although the closest orbits to Earth are Mars and Venus, Mercury is often the closest planet to Earth, since the others move away more, not being as “tied” to the Sun.
There are no seasons on Mercury like on Earth. This is due to the fact that the planet's axis of rotation is at almost right angles to the orbital plane.
As a result, there are areas near the poles that the sun's rays never reach. This suggests that there are glaciers in this cold and dark zone.
Mercury moves faster than any other planet. The combination of its movements causes the Sun to rise on Mercury only briefly, after which the Sun sets and rises again. At sunset this sequence is repeated in reverse order.
7.48×10 7 km²
6.08272×10 10 km³
3.3022×10 23 kg
5.427 g/cm³
0,38
18 h 44 min 2 s
0.119 (Bond)
31.7% potassium
24.9% sodium
9.5%, A. oxygen
7.0% argon
5.9% helium
5.6%, M. oxygen
5.2% nitrogen
3.6% carbon dioxide
3.4% water
3.2% hydrogen
Mercury in natural color (Mariner 10 image)- the planet closest to the Sun in the Solar System, orbits the Sun in 88 Earth days. Mercury is classified as an inner planet because its orbit is closer to the Sun than the main asteroid belt. After Pluto was deprived of its planetary status in 2006, Mercury acquired the title of the smallest planet in the solar system. Mercury's apparent magnitude ranges from −2.0 to 5.5, but it is not easily visible due to its very small angular distance from the Sun (maximum 28.3°). At high latitudes, the planet can never be seen in the dark night sky: Mercury is always hidden in the morning or evening dawn. The optimal time for observing the planet is morning or evening twilight during periods of its elongations (periods of Mercury's maximum distance from the Sun in the sky, occurring several times a year).
It is convenient to observe Mercury at low latitudes and near the equator: this is due to the fact that the duration of twilight there is shortest. In mid-latitudes it is much more difficult to find Mercury and only during the period of the best elongations, and in high latitudes it is impossible at all.
Relatively little is known about the planet yet. The Mariner 10 apparatus, which studied Mercury in -1975, managed to map only 40-45% of the surface. In January 2008, the interplanetary station MESSENGER flew past Mercury, which will enter orbit around the planet in 2011.
In its physical characteristics, Mercury resembles the Moon and is heavily cratered. The planet has no natural satellites, but has a very thin atmosphere. The planet has a large iron core, which is the source of a magnetic field in its totality that is 0.1 of the Earth’s. Mercury's core makes up 70 percent of the planet's total volume. The temperature on the surface of Mercury ranges from 90 to 700 (−180 to +430 °C). The solar side heats up much more than the polar regions and the far side of the planet.
Despite its smaller radius, Mercury still exceeds in mass such satellites of the giant planets as Ganymede and Titan.
The astronomical symbol of Mercury is a stylized image of the winged helmet of the god Mercury with his caduceus.
History and name
The oldest evidence of observations of Mercury can be found in Sumerian cuneiform texts dating back to the third millennium BC. e. The planet is named after the god of the Roman pantheon Mercury, analogue of Greek Hermes and Babylonian Naboo. The ancient Greeks of Hesiod's time called Mercury "Στίλβων" (Stilbo, the Shining One). Until the 5th century BC. e. The Greeks believed that Mercury, visible in the evening and morning skies, were two different objects. In ancient India, Mercury was called Buddha(बुध) and Roginea. In Chinese, Japanese, Vietnamese and Korean, Mercury is called water star(水星) (in accordance with the ideas of the “Five Elements”. In Hebrew, the name of Mercury sounds like “Kohav Hama” (כוכב חמה) (“Solar Planet”).
Planet movement
Mercury moves around the Sun in a fairly elongated elliptical orbit (eccentricity 0.205) at an average distance of 57.91 million km (0.387 AU). At perihelion, Mercury is 45.9 million km from the Sun (0.3 AU), at aphelion - 69.7 million km (0.46 AU). At perihelion, Mercury is more than one and a half times closer to the Sun than at aphelion. The inclination of the orbit to the ecliptic plane is 7°. Mercury spends 87.97 days on one orbital revolution. The average speed of the planet's orbit is 48 km/s.
For a long time it was believed that Mercury constantly faces the Sun with the same side, and one revolution around its axis takes the same 87.97 days. Observations of details on the surface of Mercury, carried out at the limit of resolution, did not seem to contradict this. This misconception was due to the fact that the most favorable conditions for observing Mercury repeat after a triple synodic period, that is, 348 Earth days, which is approximately equal to six times the rotation period of Mercury (352 days), therefore approximately the same surface area was observed at different times planets. On the other hand, some astronomers believed that Mercury's day was approximately equal to Earth's. The truth was revealed only in the mid-1960s, when radar was carried out on Mercury.
It turned out that a Mercury sidereal day is equal to 58.65 Earth days, that is, 2/3 of a Mercury year. This commensurability of the periods of rotation and revolution of Mercury is a unique phenomenon for the Solar System. It is presumably explained by the fact that the tidal action of the Sun took away angular momentum and retarded the rotation, which was initially faster, until the two periods were related by an integer ratio. As a result, in one Mercury year, Mercury manages to rotate around its axis by one and a half revolutions. That is, if at the moment Mercury passes perihelion a certain point on its surface is facing exactly the Sun, then at the next passage of perihelion the exact opposite point on the surface will be facing the Sun, and after another Mercury year the Sun will again return to the zenith above the first point. As a result, a solar day on Mercury lasts two Mercury years or three Mercury sidereal days.
As a result of this movement of the planet, “hot longitudes” can be distinguished on it - two opposite meridians, which alternately face the Sun during Mercury’s passage of perihelion, and which, because of this, are especially hot even by Mercury standards.
The combination of planetary movements gives rise to another unique phenomenon. The speed of rotation of the planet around its axis is practically constant, while the speed of orbital motion is constantly changing. In the orbital region near perihelion, for approximately 8 days, the speed of orbital motion exceeds the speed of rotational motion. As a result, the Sun stops in the sky of Mercury and begins to move in the opposite direction - from west to east. This effect is sometimes called the Joshua effect, named after the main character of the Book of Joshua from the Bible, who stopped the movement of the Sun (Joshua, X, 12-13). For an observer at longitudes 90° away from the “hot longitudes,” the Sun rises (or sets) twice.
It is also interesting that although Mars and Venus are the closest in orbit to Earth, it is Mercury that is most of the time the closest planet to Earth than any other (since the others move away more, not being so “tied” to the Sun).
physical characteristics
Comparative sizes of Mercury, Venus, Earth and Mars
Mercury is the smallest terrestrial planet. Its radius is only 2439.7 ± 1.0 km, which is smaller than the radius of Jupiter's moon Ganymede and Saturn's moon Titan. The mass of the planet is 3.3 × 10 23 kg. The average density of Mercury is quite high - 5.43 g/cm³, which is only slightly less than the density of Earth. Considering that the Earth is larger in size, the density value of Mercury indicates an increased content of metals in its depths. The acceleration of gravity on Mercury is 3.70 m/s². The second escape velocity is 4.3 km/s.
Kuiper Crater (just below center). Photo from MESSENGER spacecraft
One of the most noticeable features of the surface of Mercury is the Plain of Heat (lat. Caloris Planitia). This crater got its name because it is located near one of the “hot longitudes”. Its diameter is about 1300 km. Probably, the body whose impact formed the crater had a diameter of at least 100 km. The impact was so strong that the seismic waves, having passed through the entire planet and focused at the opposite point on the surface, led to the formation of a kind of rugged “chaotic” landscape here.
Atmosphere and physical fields
When the Mariner 10 spacecraft flew past Mercury, it was established that the planet had an extremely rarefied atmosphere, the pressure of which was 5 × 10 11 times less than the pressure of the Earth’s atmosphere. Under such conditions, atoms collide more often with the surface of the planet than with each other. It consists of atoms captured from the solar wind or knocked out from the surface by the solar wind - helium, sodium, oxygen, potassium, argon, hydrogen. The average lifetime of a certain atom in the atmosphere is about 200 days.
Mercury has a magnetic field whose strength is 300 times less than the Earth's magnetic field. Mercury's magnetic field has a dipole structure and is highly symmetrical, and its axis deviates only 2 degrees from the planet's axis of rotation, which imposes a significant limitation on the range of theories explaining its origin.
Research
An image of a section of Mercury's surface taken by MESSENGER
Mercury is the least studied terrestrial planet. Only two devices were sent to study it. The first was Mariner 10, which flew past Mercury three times in -1975; the closest approach was 320 km. As a result, several thousand images were obtained, covering approximately 45% of the planet's surface. Further research from Earth showed the possibility of the existence of water ice in polar craters.
Mercury in art
- In Boris Lyapunov's science fiction story "Nearest to the Sun" (1956), Soviet cosmonauts land on Mercury and Venus for the first time to study them.
- Isaac Asimov's story "Mercury's Big Sun" (Lucky Starr series) takes place on Mercury.
- Isaac Asimov's stories "Runaround" and "The Dying Night", written in 1941 and 1956 respectively, describe Mercury with one side facing the Sun. Moreover, in the second story, the solution to the detective plot is based on this fact.
- In the science fiction novel The Flight of the Earth by Francis Karsak, along with the main plot, a scientific station for studying the Sun, located at the North Pole of Mercury, is described. Scientists live at a base located in the eternal shadow of deep craters, and observations are carried out from giant towers constantly illuminated by the luminary.
- In Alan Nurse's science fiction story "Across the Sunny Side", the main characters cross the side of Mercury facing the Sun. The story was written in accordance with the scientific views of its time, when it was assumed that Mercury was constantly facing the Sun with one side.
- In the anime animated series Sailor Moon, the planet is personified by the warrior girl Sailor Mercury, aka Ami Mitsuno. Her attack is based on the power of water and ice.
- In Clifford Simak's science fiction story "Once Upon a Time on Mercury", the main field of action is Mercury, and the energy form of life on it - balls - surpasses humanity by millions of years of development, having long passed the stage of civilization.
Notes
see also
Literature
- Bronshten V. Mercury is closest to the Sun // Aksenova M.D. Encyclopedia for children. T. 8. Astronomy - M.: Avanta+, 1997. - P. 512-515. - ISBN 5-89501-008-3
- Ksanfomality L.V. Unknown Mercury // In the world of science. - 2008. - № 2.
Links
- Website about the MESSENGER mission (English)
- Photos of Mercury taken by Messenger (English)
- BepiColombo mission section on the JAXA website
- A. Levin. Iron Planet Popular Mechanics No. 7, 2008
- “The closest” Lenta.ru, October 5, 2009, photographs of Mercury taken by Messenger
- “New photographs of Mercury have been published” Lenta.ru, November 4, 2009, about the rapprochement of Messenger and Mercury on the night of September 29-30, 2009
Here on Earth, we tend to take time for granted, never considering that the increments in which we measure it are quite relative.
For example, the way we measure our days and years is actually a result of our planet's distance from the Sun, the time it takes to revolve around it, and to rotate on its own axis. The same is true for other planets in our solar system. While we Earthlings calculate the day in 24 hours from dawn to dusk, the length of one day on another planet differs significantly. In some cases, it is very short, while in others, it can last more than a year.
Day on Mercury:
Mercury is the closest planet to our Sun, ranging from 46,001,200 km at perihelion (closest distance to the Sun) to 69,816,900 km at aphelion (farthest). Mercury takes 58.646 Earth days to rotate around its axis, meaning that a day on Mercury takes approximately 58 Earth days from dawn to dusk.
However, it takes only 87,969 Earth days for Mercury to circle the Sun once (aka its orbital period). This means that a year on Mercury is equivalent to approximately 88 Earth days, which in turn means that one year on Mercury lasts 1.5 Mercury days. Moreover, Mercury's northern polar regions are constantly in shadow.
This is due to its axial tilt of 0.034° (compared to Earth's 23.4°), which means Mercury does not experience extreme seasonal changes where days and nights can last for months, depending on the season. It is always dark at the poles of Mercury.
A day on Venus:
Also known as the "Earth's twin", Venus is the second most nearby planet to our Sun - ranging from 107,477,000 km at perihelion to 108,939,000 km at aphelion. Unfortunately, Venus is also the slowest planet, a fact that is obvious when you look at its poles. Whereas the planets in the solar system experienced flattening at the poles due to their rotational speed, Venus did not survive it.
Venus rotates at a speed of only 6.5 km/h (compared to Earth's rational speed of 1670 km/h), which results in a sidereal rotation period of 243.025 days. Technically, this is minus 243.025 days, since Venus's rotation is retrograde (i.e., spinning in the opposite direction of its orbital path around the Sun).
Nevertheless, Venus still rotates around its axis in 243 Earth days, that is, many days pass between its sunrise and sunset. This may seem strange until you know that one Venusian year lasts 224,071 Earth days. Yes, Venus takes 224 days to complete its orbital period, but more than 243 days to go from dawn to dusk.
Thus, one Venus day is slightly more than a Venusian year! It's good that Venus has other similarities with Earth, but it's clearly not a daily cycle!
Day on Earth:
When we think of a day on Earth, we tend to think of it as simply 24 hours. In truth, the sidereal rotation period of the Earth is 23 hours 56 minutes and 4.1 seconds. So one day on Earth is equivalent to 0.997 Earth days. It's strange, but then again, people prefer simplicity when it comes to time management, so we round up.
At the same time, there are differences in the length of one day on the planet depending on the season. Due to the tilt of the Earth's axis, the amount of sunlight received in some hemispheres will vary. The most striking cases occur at the poles, where day and night can last for several days and even months, depending on the season.
At the North and South Poles during winter, one night can last up to six months, known as the "polar night". In summer, the so-called “polar day” will begin at the poles, where the sun does not set for 24 hours. It's actually not as simple as I would like to imagine.
A day on Mars:
In many ways, Mars can also be called “Earth’s twin.” Add seasonal variations and water (albeit frozen) to the polar ice cap, and a day on Mars is pretty close to a day on Earth. Mars makes one revolution around its axis in 24 hours. 
37 minutes and 22 seconds. This means that one day on Mars is equivalent to 1.025957 Earth days.
Seasonal cycles on Mars are similar to ours on Earth, more than on any other planet, due to its 25.19° axial tilt. As a result, Martian days experience similar changes with the Sun, which rises early and sets late in the summer and vice versa in the winter.
However, seasonal changes last twice as long on Mars because the Red Planet is at a greater distance from the Sun. This results in a Martian year lasting twice as long as an Earth year—686.971 Earth days or 668.5991 Martian days, or sols.
Day on Jupiter:
Given the fact that it is the largest planet in the solar system, one would expect the day on Jupiter to be long. But, as it turns out, a day on Jupiter officially lasts only 9 hours, 55 minutes and 30 seconds, which is less than a third of the length of an Earth day. This is due to the fact that the gas giant has a very higher speed rotation approximately 45300 km/h. This high rotation rate is also one of the reasons why the planet has such strong storms.
Note the use of the word formal. Since Jupiter is not solid, his upper atmosphere moves at a speed different from the speed at its equator. Basically, the rotation of Jupiter's polar atmosphere is 5 minutes faster than that of the equatorial atmosphere. Because of this, astronomers use three reference frames.
System I is used in latitudes from 10°N to 10°S, where its rotation period is 9 hours 50 minutes and 30 seconds. System II is applied at all latitudes north and south of them, where the rotation period is 9 hours 55 minutes and 40.6 seconds. System III corresponds to the rotation of the planet's magnetosphere, and this period is used by the IAU and IAG to determine the official rotation of Jupiter (i.e. 9 hours 44 minutes and 30 seconds)
So, if you could theoretically stand on the clouds of a gas giant, you would see the sun rise less than once every 10 hours at any latitude of Jupiter. And in one year on Jupiter, the Sun rises approximately 10,476 times.
Day on Saturn:
The situation of Saturn is very similar to Jupiter. Despite its large size, the planet has an estimated rotation speed of 35,500 km/h. One sidereal rotation of Saturn takes approximately 10 hours 33 minutes, making one day on Saturn less than half an Earth day.
Saturn's orbital period is equivalent to 10,759.22 Earth days (or 29.45 Earth years), with a year lasting approximately 24,491 Saturn days. However, like Jupiter, Saturn's atmosphere rotates at different speeds depending on latitude, requiring astronomers to use three different reference frames.
System I covers the equatorial zones of the South Equatorial Pole and the North Equatorial Belt, and has a period of 10 hours 14 minutes. System II covers all other latitudes of Saturn except the north and south poles, with a rotation period of 10 hours 38 minutes and 25.4 seconds. System III uses radio emissions to measure Saturn's internal rotation rate, which resulted in a rotation period of 10 hours 39 minutes 22.4 seconds.
Using these different systems, scientists have obtained various data from Saturn over the years. For example, data obtained during the 1980s by the Voyager 1 and 2 missions indicated that a day on Saturn is 10 hours, 45 minutes and 45 seconds (±36 seconds).
In 2007, this was revised by researchers in UCLA's Department of Earth, Planetary and Space Sciences, resulting in the current estimate of 10 hours and 33 minutes. Much like Jupiter, the problem with accurate measurements stems from the fact that different parts rotate at different speeds.
Day on Uranus:
As we approached Uranus, the question of how long a day lasts became more complex. On the one hand, the planet has a sidereal rotation period of 17 hours 14 minutes and 24 seconds, which is equivalent to 0.71833 Earth days. Thus, we can say that a day on Uranus lasts almost as long as a day on Earth. This would be true if it were not for the extreme tilt of the axis of this gas-ice giant.
With an axial tilt of 97.77°, Uranus essentially revolves around the Sun on its side. This means that its north or south faces directly towards the Sun at different time orbital period. When it is summer at one pole, the sun will shine continuously there for 42 years. When the same pole is turned away from the Sun (that is, it is winter on Uranus), there will be darkness there for 42 years.
Therefore, we can say that one day on Uranus, from sunrise to sunset, lasts as long as 84 years! In other words, one day on Uranus lasts as long as one year.
Also, as with other gas/ice giants, Uranus rotates faster at certain latitudes. Therefore, while the planet's rotation at the equator, approximately 60° south latitude, is 17 hours and 14.5 minutes, the visible features of the atmosphere move much faster, completing a complete rotation in just 14 hours.
Day on Neptune:
Finally, we have Neptune. Here, too, measuring one day is somewhat more complicated. For example, Neptune's sidereal rotation period is approximately 16 hours, 6 minutes and 36 seconds (equivalent to 0.6713 Earth days). But due to its gas/ice origin, the planet's poles replace each other faster than the equator.
Considering that the planet's magnetic field rotates at a rate of 16.1 hours, the equatorial zone rotates approximately 18 hours. Meanwhile, the polar regions rotate within 12 hours. This differential rotation is brighter than any other planet in the Solar System, resulting in strong latitudinal wind shear.
In addition, the planet's axial tilt of 28.32° leads to seasonal variations similar to those on Earth and Mars. Neptune's long orbital period means that a season lasts for 40 Earth years. But since its axial tilt is comparable to Earth's, the change in the length of its day over its long year is not so extreme.
As you can see from this summary about the different planets in our solar system, the length of the day depends entirely on our frame of reference. In addition, the seasonal cycle varies depending on the planet in question and where on the planet the measurements are taken.
Here on Earth, people take time for granted. But in fact, at the heart of everything lies an extremely complex system. For example, the way people calculate days and years follows from the distance between the planet and the Sun, the time it takes the Earth to complete a revolution around the gas star, and the time it takes to move 360 degrees around its planet. axes. The same method is applicable for the rest of the planets in the Solar System. Earthlings are accustomed to thinking that a day contains 24 hours, but on other planets the length of the day is much different. In some cases they are shorter, in others they are longer, sometimes significantly. The solar system is full of surprises, and it's time to explore it.
Mercury
Mercury is the planet that is closest to the Sun. This distance can be from 46 to 70 million kilometers. Considering the fact that Mercury takes about 58 Earth days to turn 360 degrees, it is worth understanding that on this planet you will only be able to see the sunrise once every 58 days. But in order to describe a circle around the main luminary of the system, Mercury requires only 88 Earth days. This means that a year on this planet lasts approximately one and a half days.
Venus
Venus, also known as Earth's twin, is the second planet from the Sun. The distance from it to the Sun is from 107 to 108 million kilometers. Unfortunately, Venus is also the slowest rotating planet, which can be seen when looking at its poles. While absolutely all the planets in the solar system have experienced flattening at the poles due to the speed of their rotation, Venus shows no signs of it. As a result, Venus takes about 243 Earth days to go around the system’s main luminary once. It may seem strange, but the planet takes 224 days to complete a full rotation on its axis, which means only one thing: a day on this planet lasts longer than a year!
Earth
When talking about a day on Earth, people usually think of it as 24 hours, when in fact the rotation period is only 23 hours and 56 minutes. Thus, one day on Earth is equal to about 0.9 Earth days. It looks strange, but people always prefer simplicity and convenience over accuracy. However, it's not that simple, and the length of the day can vary - sometimes it's even actually 24 hours.
Mars
In many ways, Mars can also be called Earth's twin. In addition to having snowy poles, changing seasons, and even water (albeit in a frozen state), the day on the planet is extremely close in length to a day on Earth. Mars takes 24 hours, 37 minutes and 22 seconds to rotate around its axis. Thus, the days here are slightly longer than on Earth. As mentioned earlier, the seasonal cycles here are also very similar to those on Earth, so the day length options will be similar.
Jupiter
Considering the fact that Jupiter is the largest planet in the solar system, one would expect it to have incredibly long days. But in reality, everything is completely different: a day on Jupiter lasts only 9 hours, 55 minutes and 30 seconds, that is, one day on this planet is about a third of an Earth day. This is due to the fact that this gas giant has a very high rotation speed around its axis. It is because of this that the planet also experiences very strong hurricanes.
Saturn
The situation on Saturn is very similar to that observed on Jupiter. Despite big size, the planet has a low rotation speed, so one rotation period of 360 degrees takes Saturn only 10 hours and 33 minutes. This means that one day on Saturn is less than half the length of an Earth day. And, again, the high rotation speed leads to incredible hurricanes and even a constant vortex storm at the south pole.
Uranus
When it comes to Uranus, the question of calculating the length of the day becomes difficult. On the one hand, the planet's rotation time around its axis is 17 hours, 14 minutes and 24 seconds, which is slightly less than a standard Earth day. And this statement would be true if not for the strong axial tilt of Uranus. The angle of this inclination is more than 90 degrees. This means that the planet is moving past the main star of the system, actually on its side. Moreover, in this situation, one pole faces the Sun for a very long time - as much as 42 years. As a result, we can say that a day on Uranus lasts 84 years!
Neptune
Last on the list is Neptune, and here the problem of measuring the length of the day also arises. The planet completes a full rotation around its axis in 16 hours, 6 minutes and 36 seconds. However, there is a catch here - given the fact that the planet is a gas-ice giant, its poles rotate faster than the equator. The rotation time of the planet's magnetic field was indicated above - its equator rotates in 18 hours, while the poles complete their circular rotation in 12 hours.